Effect pigments are used in coatings to obtain optical effects, such as a metallic or pearlescent look. Typically, in a film of a coating comprising metallic pigments lightness is dependent on the optical geometry, whereas with coatings comprising pearlescent pigments the hue changes with the optical geometry. This complicates the characterization of the visual appearance of such coating films. A further complication in this respect is the appearance of local strong scattering spots in the coating film when it is observed from a short distance, due to the presence of pigment flakes. Whereas a solid colour can be wherein by the spectral distribution of reflectance values, coatings comprising effect pigments require taking the angular and spatial dependency into account. Hitherto, the dependency of the lightness and colour of metallic and pearlescent coatings on optical geometry was examined by using a spectrophotometer at a limited number of different measuring geometries. However, this results in an incomplete picture giving data at only a very limited number of optical geometries.
U.S. Pat. No. 5,550,632 discloses a method and an arrangement for evaluating paint films using a digital photo camera. Only one optical geometry is used per recording, and since the camera is focussed, only one flop angle. Since the appearance of a coating layer comprising effect pigments is dependent on the flop angle, this method cannot be used for the evaluation of such effect coatings in one recording.